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knockout.js的学习笔记3

上一节主要是说viewModel各个域中相互通知，本节开始介绍viewModel与节点的相互通知。

我们在body上添加如下HTML片断：

The name is <span data-bind="text: fullName" id="node"></span>

然后将第一节提到的$.applyBindings疯狂删减到这样：

$.applyBindings = function(model, node){
    var str = node.getAttribute("data-bind");
    str = "{"+str+"}"
    var bindings = eval("0,"+str);
    for(var key in bindings){//如果直接eval肯定会报错,因为它找到fullName
        console.log(key)
    }
}
window.onload = function(){
    var model = new MyViewModel();
    var node = document.getElementById("node");
    $.applyBindings(model, node)
}

意料中的失败，因为fullName在window中找不到。knockoutjs里面有一个叫buildEvalWithinScopeFunction处理此问题：

$.buildEvalWithinScopeFunction =  function (expression, scopeLevels) {
     var functionBody = "return (" + expression + ")";
     for (var i = 0; i < scopeLevels; i++) {
         functionBody = "with(sc[" + i + "]) { " + functionBody + " } ";
     }
     return new Function("sc", functionBody);
 }

然后将applyBindings 改成这样:

$.applyBindings = function(model, node){
    var str = node.getAttribute("data-bind");
    str = "{"+str+"}"
    var fn = $.buildEvalWithinScopeFunction(str,2);
    var bindings = fn([node,model])
    console.log(bindings.text == model.fullName)//到这里我们就把viewModel与节点关联起来了
}

在data-bind定义两个东西,一个是viewModel中的域，另一个是对应的操作，在这里是text！在knockout中有一个叫ko.bindingHandlers的对象，里面储放着各种操作，格式如下：

init可以猜测是用于第一次绑定元素时调用的，update是每次viewModel调用的。

现在我们是玩玩，不用大动干戈。

到这里，我们就可以把Planet Earth正确地显示在span中，但当viewModel中的FullName发生改变时，span并没有发生改变，缘由是我们没有把它们绑在一起。很简单，我们把$.applyBindings里面的逻辑都整进一个$.computed 中就行了。

View Codevar validValueType = $.oneObject("Null,NaN,Undefined,Boolean,Number,String")$.dependencyDetection = (function () {
    var _frames = [];
    return {
        begin: function (ret) {
            _frames.push(ret);
        },
        end: function () {
            _frames.pop();
        },
        collect: function (self) {
            if (_frames.length > 0) {
                self.list = self.list || [];
                var fn = _frames[_frames.length - 1];
                if ( self.list.indexOf( fn ) >= 0)
                    return;
                self.list.push(fn);
            }
        }
    };
})();
$.valueWillMutate = function(observable){
    var list = observable.list
    if($.type(list,"Array")){
        for(var i = 0, el; el = list[i++];){
            el();
        }
    }
}
$.observable = function(value){
    var v = value;//将上一次的传参保存到v中,ret与它构成闭包
    function ret(neo){
        if(arguments.length){ //setter
            if(!validValueType[$.type(neo)]){
                $.error("arguments must be primitive type!")
                return ret
            }
            if(v !== neo ){
                v = neo;
                $.valueWillMutate(ret);//向依赖者发送通知
            }
            return ret;
        }else{                //getter
            $.dependencyDetection.collect(ret);//收集被依赖者
            return v;
        }
    }
    value = validValueType[$.type(value)] ? value : void 0;
    ret(arguments[0]);//必须先执行一次
    return ret
}
 
$.computed = function(obj, scope){//为一个惰性函数，会重写自身
    //computed是由多个$.observable组成
    var getter, setter
    if(typeof obj == "function"){
        getter = obj
    }else if(obj && typeof obj == "object"){
        getter = obj.getter;
        setter = obj.setter;
        scope  = obj.scope;
    }
    var v
    var ret = function(neo){
        if(arguments.length ){
            if(typeof setter == "function"){//setter不一定存在的
                if(!validValueType[$.type(neo)]){
                    $.error("arguments must be primitive type!")
                    return ret
                }
                if(v !== neo ){
                    setter.call(scope, neo);
                    v = neo;
                    $.valueWillMutate(ret);//向依赖者发送通知
                }
            }
            return ret;
        }else{
            $.dependencyDetection.begin(ret);//让其依赖知道自己的存在
            v = getter.call(scope);
            $.dependencyDetection.end();
            return v;
        }
    }
    ret(); //必须先执行一次
    return ret;
}
function MyViewModel() {
    this.firstName = $.observable('Planet');
    this.lastName = $.observable('Earth');
    this.fullName = $.computed({
        getter: function () {
            return this.firstName() + " " + this.lastName();
        },
        setter: function (value) {
            var lastSpacePos = value.lastIndexOf(" ");
            if (lastSpacePos > 0) { // Ignore values with no space character
                this.firstName(value.substring(0, lastSpacePos)); // Update "firstName"
                this.lastName(value.substring(lastSpacePos + 1)); // Update "lastName"
            }
        },
        scope: this
    });
}
$.buildEvalWithinScopeFunction =  function (expression, scopeLevels) {
    var functionBody = "return (" + expression + ")";
    for (var i = 0; i < scopeLevels; i++) {
        functionBody = "with(sc[" + i + "]) { " + functionBody + " } ";
    }
    return new Function("sc", functionBody);
}
$.applyBindings = function(model, node){       
   
    var nodeBind = $.computed(function (){
        var str = "{" + node.getAttribute("data-bind")+"}"
        var fn = $.buildEvalWithinScopeFunction(str,2);
        var bindings = fn([node,model]);
        for(var key in bindings){
            if(bindings.hasOwnProperty(key)){
                var fn = $.bindingHandlers["text"]["update"];
                var observable = bindings[key]
                $.dependencyDetection.collect(observable);//绑定viewModel与UI
                fn(node, observable)
            }
        }
    },node);
    return nodeBind
     
}
$.bindingHandlers = {}
$.bindingHandlers["text"] = {
    'update': function (node, observable) {
        var val = observable()
        val = val == null ? "" : val+"";
        if("textContent" in node){//优先考虑标准属性textContent
            node.textContent = val;
        }else{
            node.innerText = val;
        }
        //处理IE9的渲染BUG
        if (document.documentMode == 9) {
            node.style.display = node.style.display;
        }
 
    }
}
window.onload = function(){
    var model = new MyViewModel();
    var node = document.getElementById("node");
    var nodeBind = $.applyBindings(model, node);
    $.log("+++++++++++++++++++++++++++")
    $.log(model.fullName.list[0] == nodeBind);
    $.log(model.lastName.list[0] == model.fullName);
    $.log(model.firstName.list[0] == model.fullName);
    //  $.log(model.lastName.list[0] == model.fullName)
    setTimeout(function(){
        model.fullName("xxx yyy")
    },1500)
    setTimeout(function(){
        model.fullName("111 222")
    },3000)
}

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标签: knockoutjs

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原文地址：https://www.cnblogs.com/Leo_wl/p/2554967.html